DEVICE FOR GENERATING LIGHT IN AN OPTICAL LIGHT GUIDE, COMPRISING AN OPTICAL COUPLING TO A LIGHT GUIDE

Abstract: A device for generating light in an optical light guide, wherein the device includes an optical coupling between a light source (5) and a light guide (2), wherein the light source is adapted to transmit visible light or visible and ultra-violet light, wherein the light-generating element is enclosed in a glass bubble (9), wherein the light-generating element is a light arc or an electric filament, and wherein the glass bubble has a radius which corresponds generally to the length of the light-generating element. The invention is characterized by the combination that the cross-sectional dimension of the inlet orifice (8) of the light guide (2) has respectively a length and a width which corresponds generally to or is generally greater than the respective length and width of the light-generating element of the light source (5) in the same plane as the length and width respectively of the light-generating element, and the distance between the outer surface of the glass bubble (9) and the inlet orifice (8) of the light-guide (2) is shorter than the length of the light-generating element.

Description: DEVICE FOR GENERATING LIGHT IN AN OPTICAL LIGHT GUIDE, COMPRISING AN OPTICAL COUPLING TO A LIGHT GUIDE The present invention relates to a device for generating light in an optical light guide, comprising an optical coupling to a light guide. Particularly the invention relates to transmitting light from a light source, which generates visible as well as ultraviolet light to a light guide. Visible light is transmitted with the aid of optical fibres or light guides in a number of applications within among others medical instruments such as endoscopes, laparascopes, investigatory and testing equipment, plastic curing and hardening equipment for use in dental care for instance. Corresponding industrial applications are also found. A halogen incandesce lamp or a discharge lamp is often used when transmitting light of high intensity to an optical light guide. Because the light arc or the electric filament often have a relatively large extension in comparison with the diameter of the light guide, there is often used an elliptical reflector with the light source placed in one focus and the light guide in another focus. This solution is used with endoscopes, among others. Such reflectors, however, are expensive. Another solution is to use different lens systems, although such lens systems are often less suitable because they require the electric filament or light arc of the light source to have a very small extension so as to enable the majority of the light to be focused. It is also requireed that the light delivered to the light guide is fed in at a small angle to the axis of the light guide, so as to prevent the light being scattered or spread in the light outlet orifice of the light guide. The present invention provides an alternative and highly advantageous method of delivering light from a light source to an optical light guide. The present invention enables light of high intensity to be delivered to a light guide despite the solution being very compact. This enables a light source of smaller light power to be used in comparison with the afore- described technique in the case of a given light requirement at the outlet end of the light guide, therewith reducing the extent to which cooling is required. U.S. Patent Specification No. 4,229,658 defines a lamp which is intended for use in curing plastic tooth fillings. This lamp includes a light source in the form of a discharge lamp. A filter is positioned downstream of the discharge lamp in the beam path, while the inlet orifice of a light guide is placed at a distance from the filter. Although light of course is delivered to the light guide, the majority of the light generated will not be fed into the light guide because of the relatively large distance between the light arc and said inlet end. Consequently, there is also a high cooling requirement, which is the reason for the comprehensive array of cooling fins on the housing surrounding the light source. The present invention thus relates to a device for generating light in an optical light guide, wherein the device includes an optical coupling between a light source and a light guide, wherein the light source is adapted to transmit visible light or visible and ultraviolet light, wherein the light-generating element is enclosed in a glass bubble, wherein said light- generating element is a light arc or an electric filament, and wherein the glass bubble has a radius which corresponds essen- tially to the length of the light-generating element, and wherein the device is characterized by the combination that the cross-sectional dimension of the light guide inlet orifice has a length and a width respectively which essentially correspond to or exceed the length and the width respectively of the light-generating element of said light guide in the same plane as the length and the width respectively of said light-generating element; and in that the distance between the outer wall of the glass bubble and the light guide inlet orifice is shorter than the length of the light-generating element. The invention will now be described in more detail partly with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings, in which Figure 1 illustrates schematically a light source and a light guide in accordance with a first embodiment of the invention; - Figure 2 illustrates from above part of the embodiment illustrated in Figure 1; and Figure 3 is a view corresponding to that of Figure 2 and illustrates a second embodiment of the invention. Figure 1 is a schematic illustration of a device for generat¬ ing light in an optical light guide in accordance with the present invention, said device including an optical coupling between a light source 5 and a light guide 2. The light source 5 is shown dismantled in Figure 1, in other words that which is seen is the light source 5 and its base l. The illustrated light source may be a halogen type light source or a discharge light source. In the Figure 1 illustration, the light source includes a discharge lamp which includes between the two electrodes 6, 7 a glass bubble 9 in which the tips of the electrodes are enclosed. The glass bubble has a radius which corresponds essentially to the length of the light-generating element. The light-generating element in a discharge lamp is a light arc, while in a halogen lamp it has the form of an electric filament. A discharge lamp is constructed to transmit both visible and ultraviolet light, whereas a halogen lamp will essentially transmit only visible light. The invention is characterized by the combination of features wherein the cross-sectional dimension of the inlet orifice 8 of the light guide 2 has respectively a length and a width which essentially corresponds to or exceeds respectively the length and width of the light-generating element of the light source 5 in the same plane as the length and width respective¬ ly of the light-generating element and that the distance between the outer wall of the glass bubble 9 and the inlet orifice 8 of the light guide 2 is shorter than the length of the light-generating element. In the case of the Figure 1 embodiment, the inlet orifice 8 lies against the outer wall of the glass bubble, which is the preferred embodiment. It has surprisingly been found that when using the aforedes- cribed embodiment, i.e. the embodiment in which light is fed directly from the light source into the light guide without the assistance of reflectors or lenses, much more light can be delivered to the light guide than when using known devices. It has thus been possible to increase considerably the efficiency between the light transmitted by the light source and the light delivered to the light guide. One related factor in this regard is that it has been possible to use as a light source a discharge lamp having a very short electrode dis¬ tance. Lamps of this nature were produced first in recent times and then particularly for the automotive industry. Such lamps have an electrode distance of roughly only 3 millime¬ ters. Thus, in this regard, the electrode distance is of the same order as the diameter of a light guide suitable for the intended purpose. The outer diameter of the glass bubble of such a lamp is about 6-7 millimeters. According to one preferred embodiment of the invention, the light source is comprised of a discharge lamp having an electrode distance of less than 4 millimeters, preferably 3 millimeters. Thus, when a light guide is used which has a diameter of from 3-4 millimeters, for instance, while placing at the same time the inlet orifice of the light guide close to the glass bubble, so much light will be delivered that, as said above, the efficiency degree will be considerably greater than that obtained with known techniques in which expensive elliptical reflectors are used together with discharge lamps which have greater, conventional electrode distances. Figure 3 illustrates a second embodiment of the invention in which the aforesaid light guide is comprised of two or more separate light guides 10, 11, 12. These light guides have together a cross-sectional dimension which has a length and a width respectively which corresponds essentially to or is greater than the length and the width of the light-generating element of the light source respectively in the same plane as the aforesaid length and width respectively of the light- generating element. The inlet orifice of respective light guides 10, 11, 12 are placed adjacent one another and tangen- tially in relation to the outer surface of the glass bubble 9. This embodiment enables a further quantity of light to be delivered to the light guides. These light guides can be coupled to one single light guide after a given length. The embodiment shown in Figure 3 comprises three light guides, although it will be obvious that further light guides may be arranged around the glass bubble 9. Light sources of the aforesaid kind generate a considerable amont of heat. According to one preferred embodiment of the invention, however, the light guide 2 is made of a material which is capable of withstanding the temperature to which the inlet orifice of the light guide 2 is heated without needing any special cooling. The material used is preferably a quartz material. A light guide normally has a circular cross-section. The light arc of a discharge lamp, however, has generally an ellipsoidal configuration, with a major axis which is much longer than the minor axis. For instance, a light arc which has a length of 3 millimeters may have a largest width of 1.5 millimeters. In accordance with one advantageous embodiment of the invention, the light guide or light guides therefore has or have a cross- section which deviates from a circular shape and which has a larger dimension in the longitudinal direction of the light- generating element than in a direction perpendicular thereto. For instance, at least the inlet end of the light guide may have a correspondingly elliptical cross-sectional shape so as thereby to capture more light from the light source than that which is captured with a light guide that has the same surface area but is circular in cross-section. Such a light guide whose inlet end has an elliptical cross-sectional shape may transform to a circular cross-sectional shape successively along its length, such that its outlet end will have a circular cross-section. According to one preferred embodiment of the invention, the efficiency of the device is still further enhanced by placing a reflector 13 adjacent the glass bubble on the opposite side of the light guide 2, this reflector being intended to reflect light into the light guide through the medium of the glass bubble 5. According to one embodiment, the reflector is a separate unit which is placed close to or in contact with the glass bubble 9. However, one preferred embodiment of the invention includes a reflector 13 in the form of a reflecting layer or surface applied to the outside of the glass bubble 9 on the side thereof opposite to the light guide 2. The layer 13 functions to reflect light into the light guide 2 through the medium of the glass bubble. According to another preferred embodiment of the invention, the layer 13 is intended to reflect light generally of those wavelengths that are desired in the light guide 2, and to transmit light of wavelengths undesirable in the light guide 2. This is achieved by appropriate choice of layer composi¬ tion. The layer 13 may consist of Rhodium when high reflection of ultraviolet light is required while, at the same time, achieving a high transmission of visible light. Furthermore, different layers of mutually different compositions may be placed one upon the other so as to form together a reflective and transmittal layer of desired optical properties. The properties of different compositions are themselves known and knowledge thereof is generally available, and hence this aspect will not be described in detail here. According to one highly preferred embodiment of the invention, the layer 13 is adapted to reflect ultraviolet light and to transmit an essential part of the visible light. As mentioned in the aforegoing, the light guide 2 which lies proximal to the light source must be capable of withstanding the temperature to which the inlet end thereof is heated. Quartz is a suitable material in this regard. However, it may be desirable to construct the major part of the light guide from some other material, for instance a plastic material. For this reason, in accordance with one embodiment, the outlet end 14 of the light guide 2 is connected to a second light guide 4 in which the light can be conveyed further. This second light guide 4 may also be a liquid-filled light guide. When it is desired to filter the light transmitted from the light source, one or more filters 3 are provided between the first-mentioned light guide 2 and the second light guide 4, in accordance with one preferred embodiment. This avoids positioning a filter or filters between the glass bubble 9 and the inlet orifice 8 of the first-mentioned light guide 2, the presence of such a filter or filters resulting in an increase in the distance between the light-generating element and the inlet orifice 8 and therewith in lower efficiency. Further¬ more, filters are normally unable to withstand those tempera¬ tures that prevail in the proximity of the glass bubble. According to one alternative embodiment, one or more corres- ponding filters 15 is/are placed in the beam path of the light outlet orifice 16 of the last light guide 4. This can be seen from Figure 2, in which such filters 15 have been indicated in broken lines. Such a filter may be fitted onto the tip of the light guide and may be constructed so as to enable a shift to be made readily between filters of different properties, depending upon the use concerned. Filters can also be used to filter-off undesirable parts of the spectrum generated by the light source. The need for and the choice of filters will, of course, depend on the applica¬ tion concerned. So-called UVA-radiation and UVB-radiation are filtered-off in many applications. In other instances, it may be desired to reduce thermal radiation, in which case a so- called IR-blocking filter is used. In other instances, it may be desirable to filter-off visible light and to retain ultraviolet light. Woods glass is used in cases such as these. When applying the invention to cure, or harden, dental filling material, the filter is constructed essentially to transmit light having a wavelength range of 400-480 nanometers. UVA- radiation is sometimes used instead in the case of certain dental filling materials. It will therefore be seen that the present invention solves the drawbacks mentioned in the introduction and provides a highly efficient, extremely compact and simple device. The invention is suited for all applications and then particularly for applications in which ultraviolet or blue-violet light is used. One example of such use is found in the curing of plastic materials in dental care. Although the invention has been described with reference to a number of exemplifying embodiments thereof, it will be understood that the invention can be modified still further in ways obvious to the person skilled in this art. The invention is not therefore restricted to the aforedeε- cribed and illustrated embodiments thereof since modifications and variations can be made within the scope of the following Claims.

Claims: CLAIMS 1. A device for generating light in an optical light guide, said device including an optical coupling between a light source (5) and a light guide (2) , wherein the light source is adapted to transmit visible light or visible and ultra-violet light, wherein the light-generating element is enclosed in a glass bubble (9) , wherein the light-generating element is a light arc or an electric filament, and wherein the glass bubble has a radius which corresponds generally to the length of the light-generating element, said device being character¬ ized by the combination that the cross-sectional dimension of the inlet orifice (8) of the light guide (2) has respectively a length and a width which corresponds generally to or is generally greater than the respective length and width of the light-generating element of the light source (5) in the same plane as said length and width respectively of the light- generating element, and the distance between the outer surface of the glass bubble (9) and the inlet orifice (8) of the light guide (2) is shorter than the length of the light-generating element. 2. A device according to Claim 1, characterized in that the light guide (2) includes two or more mutually separate light guides (10, 11, 12) which have together a cross-sectional dimension which includes a length and a width respectively which correspond generally to or which are generally greater than the respective length and width of the light-generating element of the light source (5) in the same plane as the length and width respectively of said light-generating element; and in that each of the inlet orifices of respective light guides (10, 11, 12) are placed adjacent one another and tangentially in relation to the outer surface of the glass bubble (9) . 3. A device according to Claim 1 or 2, characterized in that the light guide (2) or the light guides (10, 11, 12) has/have a cross-sectional shape which deviates from a circular shape and which has a larger dimension in the longitudinal direction of the light-generating element than in a direction perpendic¬ ular thereto. 4. A device according to Claim 1, 2 or 3, characterized in that the light guide (2; 10, 11, 12) is made from a material which is able to withstand the temperature to which the inlet orifice of the light guide is heated without requiring separate cooling, preferably a quartz material. 5. A device according to Claim 1, 2, 3 or 4, characterized in that the light source (5) is a discharge lamp having an electrode distance shorter than 4 millimeters, preferably 3 millimeters. 6. A device according to Claim 1, 2, 3, 4 or 5, character¬ ized by a reflector (13) positioned adjacent the glass bubble (9) on the side thereof opposite to the light guide (2; 10, 11, 12) , said reflector being intended to reflect light into the light guide through the medium of the glass bubble. 7. A device according to Claim 1, 2, 3, 4 or 5, character¬ ized by a reflector (13) in the form of a reflective layer provided on the side of the glass bubble (9) opposite to the light guide (2; 10, 11, 12), said layer being intended to reflect light into the light guide through the medium of the glass bubble. 8. A device according to Claim 8, characterized in that the layer (13) is intended essentially to reflect light of wavelengths desired in the light guide (2; 10, 11, 12) and to transmit light of wavelengths undesirable in the light guide. 9. A device according to Claim 8, characterized in that the layer (13) is adapted to reflect ultraviolet light and to transmit a substantial part of the visible light. 10. A device according to any one of the preceding Claims, characterized in that the outlet end (14) of the light guide (2; 10, 11, 12) is connected to a second light guide (4) in which the light is further transported. 11. A device according to Claim 10, characterized in that one or more filters (3) is/are positioned between the first- mentioned light guide (2; 10, 11, 12) and said second light guide (4) . 12. A device according to any one of Claims 1-10, character¬ ized in that one or more filters (15) is/are placed adjacent the light outlet orifice (16) of the last light guide (4) in the beam path.

Inventors: FAST PEDER, FAST, PEDER
Applicants: FAST PEDER, ULTRALUX AB, FAST, PEDER
Application year: 1994
Main classification: G02B6
IPC codes: G02B6